Midnight Hour

I've heard some talk about this on this board and from an FD owner I personally know. Can someone explain to me how these two are alike?

Brandon

maxcooper

The rotary has a full four-stroke style power cycle, so in a basic sense it is more like a four-stroke. But, it does have some similarities to two-strokes. Each rotor fires once per main shaft revolution (remember each rotor has three chambers -- each chamber fires once every three rotations). It has ports on the combustion chamber walls rather than valves. It's loud!

-Max

RICE RACING

It smells like a chainsaw

It sounds like a chainsaw

It cuts through a HONDA just like a chainsaw

Rotaries are a two cycle four stroke, as Maxcooper said they have a true 4 cycle (combustion event) but unlike a piston 4 cycle engine the Wankel rotary only needs one crank shaft revolution to complete its cycle, just like a two stroke piston engine.

Pretty easy huh

Midnight Hour

Wow...that's easy enough. Thanks guys.

Brandon

Judge Ito

Easy???? yeah right the rotary engine is a very unique little.. big, little,big,little,big engine... 4 cycle but act's like a 2 cycle with a 6 cil. power stroke. pretty easy huh?

Jeff20B

iTrader: (13)

I tend to refer to it as a '3 stroke' because the rotors have 3 faces, there is an intake section, a combustion section, and an exhaust section (3 again) in three very different locations inside the engine. The 4 stroke theory of suck, squease, bang, blow is sorta happening in 3s in a rotary. There are no valves to 'tell' it when to do its thing, so it sucks and starts to squease at the same time (this is where forced induction really earns its keep), then bangs while continuing to squease (a couple of times mind you with L/T and wasted spark, or lack thereof), then basically blows for a lot of º. That looks like three to me hehe!

I think the problem lies in trying to fit a rotary into a piston mold when it obviously is a different animal, and therefore deserves different status. Sure there are some similarites to boingers such as they are both engines, both use spark plugs etc. Hmm, using that logic we can see that a VW bug and an REPU both have four tires and two doors. That doesn't mean a truck is an underpowered sedan, nor does it mean a VW is a Mazda (but putting a Mazda rotary into a bug sure is fun!!!).

Heh, suck squease bang blow lol!

duboisr

The rotory is geared 3to 1 not 4to 1 or2to 1 any way they are fast and fun .A 150 pound block that can turn 8000 rpm and put out big power.

Jeff20B

iTrader: (13)

That's right. I forgot about the stationary gearing being 3 to 1. Heh, even more pro 3 stroke info

Cheers!

it drinks gas like a v-8 though

KevinK2

Yes, 4-stroke engine with ports instead of valves.

But a complete cycle of a rotor face requires 3 crank revolutions. So the Wankel requires 3 crank revolutions to complete it's cycle, vs 2 revs for a boinger.

Jeff20B

iTrader: (13)

3 stroke

rotard

Drinks oil like a 2 stroke. And some guys mix their gas like a 2 stroke.

Jeff20B

iTrader: (13)

That's only because of the apex seals; which by the way, are three per rotor.

RICE RACING

To answer your question

2 stroke piston engine, completes its full cycle in one engine RPM
so does the wankel rotary

2 stroke piston engine for it's displacement breaths twice as much as a 4 stroke piston engine by the time both complete one power cycle
so does the wankel rotary

All of this talk realy confuses the issue, a wankel is pretty much the same as a 2 stroke in that it basically does double of the work of an equivalent 4 stroke piston engine. Hence you realy need to double the 1.3lt everyone uses to describe the 13B cause most have no idea that it is like a two stroke in this regard.

If you use any known convention forumlas for figuring out gas flow dynamics you need to double the displacement for a wankel because it has a 4 stroke cycle (in that there are 4 distinct events) but does it twice as often in 2 crank rpm.

Easy as that.

BuiltForBoost

Well, a 4 stroke 4banger fires twice per 1 rpm and so does the 2 rotor correct? A 2 stroke 4banger fires 4 times per rpm. Doesn't this contradict the 2 stroke comparison and make the 2 rotor more like a regular 4 stroke 4cyl?

It takes 2 rpm to fire all the pistons in a 4 stroke yet 3 rpm to fire all rotors. But with a 4 chamber 4 cyl motor vs the 6 chamber 2 rotor you end up with the same amount of combustion per rpm.

-Kevin

Evil Aviator

Yes, you are correct in that the 2-rotor fires like a 4-cylinder 4-stroke engine. In fact, you can set an aftermarket tachometer or EMS to "4-cylinder mode" and it will work with a 2-rotor engine. No, this doesn't contridict the 2-stroke comparison. The 2-stroke comparison is between a 2-cylinder engine and a 2-rotor engine of the same rated displacement. What you are missing here is that the rotary engine rated displacement is based on one output shaft revolution (as is a 2-stroke engine), not three.

FYI, the rotary engine doesn't have any "strokes". It has its own cycle, called a "rotary cycle" or "Wankel cycle".

Jeff20B

iTrader: (13)

Even though the term 'stroke' does not really apply to a rotary, I still like to call it a 3 stroke to mess with all the boinger-heads out there.

NZConvertible

The rotary engine doesn't have it's own cycle. Everyone's thinking about 2-strokes and “3-strokes” (oh, jeez...), but you just have to think about what actually happens inside the engine on a simpler scale. A small volume gets bigger (intake), then smaller (compression), then bigger again (combustion), the smaller again (exhaust), then repeats. That’s the Otto cycle (commonly referred to as the 4-stroke cycle), not the rotary cycle. There is no difference in this basic cycle between piston and rotary engines; they simply use a different mechanical method to achieve the volume changes and port opening. Using the word “stroke” when talking rotaries may not be great English (sweep maybe?), but as an engineering term it is still completely correct.

Evil Aviator

The Wankel cycle is a derivative of the Otto cycle, just as the Miller cycle is also a derivative of the Otto cycle. However, the Wankel cycle is still its own cycle, even though it is a type of Otto cycle. Nice try, though.

Stroke: The distance traveled by a piston from the top to the bottom of its stroke.

Evil Conclusion: No pistons = no strokes.

Wankel engine = 4 stages, 5 events, 0 strokes.

Edit - this link may help:
http://www.geocities.com/evilaviator/rotarycycle.html

WackyRotary

No, no, no, no. A rotary has a 2-1/5 cycle's.

But seriously as someone sort of mentioned, its NOT a
2-stroke, but its NOT a 4-stroke engine. Its revolutionary and not related to the other two engines directly. However, they are all IC engines(internal combustion engines that are a special kind of air pump that harnesses pressures created when volitial gases are ignited at the aproiate time after being compressed) that produce shaft rotation. THe only difference between the 2-stroke, 4stroke compared to the rotary is that it produces shaft rotatation a completely different way.

NZConvertible

Sorry, but I have to disagree. Your article even backs me up. It clearly states a couple of times that there are four "stages", and these are the same four stages that take place in a 4-stroke piston engine. The article calls it the "Wankel Cycle", but this is a reference to the mechanical method of increasing and decreasing the volume of the chamber. It is not a correct reference to a thermodynamic cycle (like the Otto, Diesel, Brayton or Rankine cycles). Don't get mechanical cycles and thermodymanic cycles mixed up. You're right that the Miller cycle is a derivative of the Otto cycle, but the Wankle rotary engine is a 4-stroke, Otto cycle engine. If you plotted the P-V diagram, you'd see it's the same as a 4-stroke piston engine (whereas the Miller cycle has a distinctly different P-V digram).Huh? What's this 5th event?

TommyTheCat

If anyone cares: go to www.howstuffworks.com for an explanation. They have lots of usefull info for all kinds of stuff(even besides cars).

Evil Aviator

5 Events - Physics 101:
1) Intake
2) Compression
3) Ignition
4) Power
5) Exhaust

Yes, the Wankel cycle has 4 stages. The Diesel and Miller cycles also have 4 stages. So are the Diesel and Miller cycles considered Otto cycles in NZ? I think what you are missing is that the term "cycle" may involve both the thermodynamic and mechanical aspects of an engine. Hehehe, I must admit that the P-V diagram was an excellent longshot to try to distance the Miller from the Otto. I can hardly wait to see a P-V on the Renesis.

What, no arguements about the Wankel being a hybrid of an Otto and Brayton cycles? How about the rotary Sterling cycle engine - is it a Wankel or a Sterling or both? How about the old arguement that the Wankel "stroke" is defined by 2x the offset of the crank pins as it is also sometimes defined on a piston engine?

KevinK2

5 events? why not include intake and exh open and close events for a total of 9?

main problem is too much emphasis on words like cycle and stroke, which are non specific terms. ex, you can have 'power' and 'return' strokes when rowing a boat, no pistons needed. One can buy 2-cycle oil for a 2-stroke heat engine. Just words.

Hopefully u know Brayton refers to 'turbine cycles' that continuously produce power with no crankshaft needed. and the sterling engines use external heat and no combustion products.

The 'otto cycle' can refer to the P-V behavior of any heat engine with the same 4 thermodynamic steps. The wankel engine has an otto cycle P-V curve, the 4 stroke diesel does not.

'The otto cycle engine' strictly speaking, is the single piston si 4 stroke, IC heat engine that otto made.

AlmightyRX3

not to sound stupid, but they really arent any type of "Stroke" considering a 4 stroke and 2 stroke engine have the term STROKE derived fromt eh stroke of a crankshaft moving the piston up and down. Rotaries dont have a stroke .